The goal of this research is to study the within-muscle heterogeneity of blood flow kinetics in normal legs and in legs with arterial disease for the purposes of : 1. improving our understanding of blood flow kinetics in the normal and diseased state; 2. providing a mathematical model which allows more accurate data analysis of diagnostic data; 3. determining the power of the within muscle heterogeneity, as compared with that of existing methods, in diagnosis of peripheral vascular disease. A new mathematical model has been developed which will allow estimation of the heterogeneity of flow kinetics within a muscle using washout of an injected tracer. An existing data base from a previous study will provide the material for analysis.